#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2019 crane <crane@gosun>
#
# Distributed under terms of the MIT license.

"""

"""

def trans(s):
    l = len(s)
    if l == 1:
        return s[0]+s[1]
    if l == 0:
        return ""

    return s[0]+s[l-1] + trans(s[1:-1]) + s[l-1]+s[0]


def main():
    print("start main")
    v = trans("1234")
    print(v)

if __name__ == "__main__":
    main()
